<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>teacherJs</title>

</head>
<body>
        <!-- HTML结构 -->
        <p class="js">JavaScript</p>
        <div class="list">
            <p id="java">Java</p>
            <p id="python">Python</p>
            <p id="scheme">Scheme</p>
        </div>

    <script src="js/FirstHtmlJS.js">
        // <script>
       var     js = document.getElementsByClassName('js')[0];
       var list = document.getElementsByClassName('list')[0];


    </script>

        <script type="text/javascript">

            eval("x=10;y=20;document.write(x*y)")
            document.write("<br />")

            document.write(eval("2+2"))
            document.write("<br />")

            var x=10
            document.write(eval(x+17))
            document.write("<br />")

            eval("alert('Hello world')")

        </script>
</body>
</html>